This FAQ page from the Teacher2Teacher service at The Math Forum @ Drexel contains links to many resources offering ideas for celebrating the 100th Day of School. Resources include T2T discussions, children's literature, teacher resource books, and web sites.

In this 8-lesson unit students use buttons to explore logical and numerical relationships that form the conceptual basis for understanding addition and subtraction operations. Topics include counting, ordinal numbers (and relative position), classification (attributes), relationships between numbers, addition of sets, commutativity of addition, sums to 10, fact families (including subtraction), three models of subtraction ("take away", comparative, missing addend), and bar graphs. Includes student activity sheets and a link to an online graphing applet.

This interactive 100 grid has a variety of open-ended uses. Users can "make" as many counters as they choose from among three different kinds, and then drag them onto the grid, allowing any number to be covered by up to 3 different markers at one time. An Ideas page offers possible tasks and games suited to the applet.

This webpage discusses the extension of children's counting skills beyond 10. It illustrates the difficulties resulting from the irregularity of English number names in the teens as well as the challenge of maintaining one-to-one correspondence with larger numbers. Several teaching strategies and activities are suggested to help students overcome these difficulties.

In this 5-minute video Laura Domalik defines number sense and provides instructional strategies for counting and vocabulary, including counting on, counting back, one more than (+1), one less than (-1), basic fact concepts of +1 and -1, and missing addends. She demonstrates a game called Garbage, which can be played alone or with a partner.

This narrative document describes the progression of Counting and Cardinality and Operations and Algebraic Thinking across the K-5 grade band. It is informed both by research on children's cognitive development and by the logical structure of mathematics. The document discusses the most important goals for elementary students that of understanding and using numbers. The focus is on the basic operations—the kinds of quantitative relationships they model and consequently the kinds of problems they can be used to solve as well as their mathematical properties and relationships.

Students can use this interactive Flash applet to practice subitizing and counting groups of objects, to understand the importance of 5 in our base-10 number system, and to learn basic addition facts. In the four included games students construct groups of 5 objects, add groups of objects within 10, and identify and record numbers within 10. Auditory prompts support students with limited reading ability.

Ten bones are hidden in the squares of a blank 1-100 grid. Students are given the numbers of the squares one at a time. They attempt to locate the numbers in the hundreds chart and find all 10 bones within 60 seconds. Numbers of the incorrectly guessed squares are left in place to help with the search. The game helps students understand the structure and patterns of our base-10 number system. Children can be encouraged to make use of a found bone to locate the next one.

This intereactive Flash applet helps children learn grouping, tally marks, place value, addition, and subtraction. Students help the alien spaceship move cows into corrals by counting by 5s and 10s. They also can apply those grouping skills to practice adding and subtracting two-digit numbers with regrouping. Audio cues and prompts reinforce the user's actions and facilitate counting and the development of math language.